The present invention relates to the improvement of hybrid vehicles, i.e. vehicles associating electric and thermal drive, when the end purpose of dual drive is to increase the energy efficiency. It more particularly relates to vehicles built around planetary gear mechanisms known as of “power derivation” or “power distribution”, when they are used as the power distribution integration system. This last is very useful to manage the power distribution between the electric and the thermal sources. They should not be confused with planetary gear mechanisms used for power transmitting system from an input shaft to an output shaft. These last, known as of “power transmission”, have a typical arrangement with one of their three shafts blocked in rotation to their fixed casing. They are generally used as rotation speed adaptors between two shafts and can be replaced by gears, chains, belts and so on . . .
For instance, the patents WO 2006/098249 A1, US 2010/262322 A1, WO 2007/093882 A2, WO 2005/118322, WO 2005/118322 A1, US 2009/314565 A1 describe directly or indirectly such vehicles based on one power distribution integration system which can be a planetary gear mechanism of “power derivation” type as their preferred mode of realization. They may also use some planetary gear mechanisms of the second type to adapt the rotation speeds of shafts but their function and their arrangement are quite different so they should not be confused with the first type.
In the following text, we only consider planetary gear mechanisms of “power derivation” type. In addition, out of their three shafts, the shaft which has the controlled torque is the pilot shaft. To simplify the talk, “the pinion gear” means “the pinion gear itself and its symmetrical or its counterparts which have the same function in the planetary gear mechanism.
The improvement of the efficiency of current hybrid vehicles is based on three main ideas, namely:                to make the thermal engine runs at its optimal torque and rotation speed regarding its efficiency,        to recover the kinetic energy of the vehicle during its deceleration,        to turn off the thermal engine during period when the vehicle is at a standstill.        
The first main idea is founded on the observation of the ISO efficiency chart for a thermal engine which shows a better efficiency at high torque and slow rotation speed for the same output power. The insertion in the power transmitting system of a planetary gear mechanism associated with a means to import or to export electric energy makes it possible to adjust the operating torque and rotation speed of the thermal engine in order to keep them in the optimal efficiency zone. The device according to the present invention uses this known technique but, as we will see, it draws much more benefit from it.
Hence, in a typical hybrid vehicle, a large part of the mechanical energy is transformed into electric energy in a generator and then stored in a battery. Later this energy is restored and reconverted in mechanical energy in an electric motor according to the power requirements of the vehicle. These successive energy transformations have an efficiency of about 80% for the best equipment and provided that the main part of the energy does not go through the battery stage. This efficiency naturally affects the global efficiency of the vehicle. Whereas the highest efficiency of a thermal engine is 35%, the efficiency of a hybrid vehicle reaches a maximum of 25%. It is thus beneficial to minimize the relative quantity of mechanical energy transformed into electricity which is then degraded in the successive transformations. We will see how the present invention minimizes the quantity of electricity generated and especially the quantity stored in the battery.
The Willis formula related to planetary gear mechanism shows that the rotation speed of the output shaft depends of the rotation speed of the pilot shaft, i.e. the third shaft of the planetary gear mechanism, and the rotation speed of the input shaft. The graph is a straight line having the gear ratio for directing coefficient, therefore for “slope”. This straight line is the “characteristic” of the planetary gear mechanism. On startup of the vehicle, the electric motor provides all the power. To obtain the maximum torque, the “characteristic” must be as horizontal as possible, the horizontal one being the direction of the axis of the pilot shaft speed. This is important because the startup torque dimensions the power of the whole electric chain. Conversely, the “characteristic” must be as vertical as possible in order to reach high vehicle speeds, the vertical one being the direction of the axis of the output shaft speed. These two criteria are contradictory and in general lead to a compromise prejudicial to the efficiency and to the power of the electric equipment's. We will see how the device according to the present invention circumvents this compromise.
To reach high vehicle speeds, the current hybrid vehicles may have to extend the useful field of their “characteristic” by reversing the rotation direction of the pilot shaft. This inversion happens at usual speeds on highway whereas the needs for power are important and while the efficiency around this point is poor. We will see later why the present invention does not have to reverse the direction of the pilot shaft to reach high vehicle speeds.
Current hybrid vehicles must increase their electric autonomy and find additional power from an electric source at high vehicle speed. Consequently they need huge electric storages and that for long runs, this means big batteries. We will see why the present invention avoids these difficulties.